Systemic lupus erythematosus (SLE) is characterized by autoantibodies against proteins that make up small nuclear ribonucleoproteins (snRNPs). snRNPs are components of spliceosomes, cellular organelles that splice non-coding regions (introns) out of pre-mRNA to form mature mRNA. In general mRNA splicing is rigidly defined through interactions of snRNPs and snRNP-associated proteins with (cis) elements on pre-mRNA. In contrast, in some genes one or more introns can be spliced in more than one way. This process is referred to as alternative splicing. Studies to date have indicated that alternative splicing is regulated through protein interactions with constitutive spliceosome proteins and pre-mRNA. Regulation of alternative splicing leads to the synthesis of proteins with different functions and thus is an important mechanism in regulating gene expression. Although much is known about genes that are alternatively spliced, little is known about genes that regulate this process. We have recently identified a new autoantigen (SWAP) that is homologous to a Drosophila gene (su[w/a]) that regulates alternative splicing. su(w/a) autoregulates splicing of su(w/a) pre-RNA and SWAP produces similarly alternatively spliced mRNAs, suggesting that SWAP is also a splicing regulator. Antibodies to snRNPs in SLE patients are directed against multiple epitopes of targeted snRNP proteins, and thus may reflect a process of auto-immunization to these particles. We have shown that SWAP antibodies are similarly directed against multiple epitopes on the protein, but are found in normal as well as autoimmune patients. Our hypothesis is that these antibodies result from a process of normal autoimmunization. The restricted cellular distribution of this splicing regulator may point to a cellular source of normal snRNP immunization. We propose to extend studies of the function of and autoimmunity to SWAP. T-cell dependence of SWAP autoantibody production. The age at which antibody production to SWAP autoantibody production in normal humans. Questions regarding both autoimmunity and function will be explored through analyses of the distribution of SWAP mRNA and protein expression. This will include analyses of expression in cells undergoing apoptosis and activated antigen presenting cells, cellular events potentially associated with autoimmune responses. Molecular studies will determine whether SWAP autoregulates splicing of SWAP pre-mRNA and explore how this protein interacts with other snRNP proteins to regulate splicing. The developmental effects of SWAP will be explored by creating transgenic mice, overexpressing a SWAP transgene. To further define SWAP splicing regulation in the context of physiologically important alternative splicing, its effect on the alternative splicing of CD45 and bcl-x splicing will be studied.